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I explained this to >> you before and this thing needs to be tied on the LAZY bit otherwise a >> SCHED_OTHER task can prevent a real-time task from running, which is >> fundamentally wrong. > > So here we disagree, I don't want this tied to LAZY. > > SCHED_OTHER can already inhibit a RT task from getting ran by doing a > syscall, this syscall will have non-preemptible sections and the RT task > will get delayed. > > I very much want this thing to be limited to a time frame where a > userspace critical section (this thing) is smaller than such a kernel > critical section. > > That is, there should be no observable difference between the effects of > this new thing and a syscall doing preempt_disable(). > > > That said; the reason I don't want this tied to LAZY is that RT itself > is not subject to LAZY and this then means that RT threads cannot make > use of this new facility, whereas I think it makes perfect sense for > them to use this. Thinking out loud: I know we are trying to keep the overhead to a minimum but is it acceptable to go through with schedule() and decide on extending the time slice in pick_next_task_fair() / pick_task_rt()? Then, a higher priority task can always preempt us when preemption is enabled and between the tasks of same class, it is just a redundant schedule() loop. It'll require some additional care to start accounting for delay from the time when NEED_RESCHED was set and not when schedule() is actually called but would the overhead be that bad? Or would we like to prevent preemption from RT tasks too on !PREMMPT_RT since whatever the task asking for the extended slice is doing is considered important enough? -- Thanks and Regards, Prateek